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REVIEW PAPER ON ANTENNA DESIGN AND SIMULATIONSurbhi Soni, (M.Tech Scholar) Asst. Prof. Saurabh Pateriya
Abstract - Antenna is the most vital half in wireless communication systems. Antenna transforms electrical signals into radio waves and the other way around. The antennas are unit of assorted types and have completely different characteristics in line with the requirement of signal transmission and reception. during this paper, we tend to gift comparative analysis of assorted kinds of antennas that may be differentiated with relation to their shapes, material used, signal information measure, transmission vary etc. Our main focus is to classify these antennas in line with their applications. As within the epoch antennas area unit the essential conditions for wireless communications that's needed for quick and economical communications. This paper can facilitate the look designer to decide on the correct antenna for the required application. Microstrip patch antennas are mostly used in modern communication devices over conventional antennas mainly because of their size. In this review paper a survey is conducted on commonly used techniques and design used in microstrip antenna papers which has been used by authors for designing of an efficient, low profile, small, compatible, affordable microstrip antenna, mainly used to designed reconfigurable, multiband and wideband antennas, after that a initiator patch design is given with dimensions on which technique will be applied for the analysis of different parameter of antenna.
Keywords: Fractal, Slot, Dielectric, Microstrip, DGS.
1. INTRODUCTION
All antennas can be called as dedicated transducers as these converts radio- frequency (RF) signals into alternating current (AC) or vice-versa. There are two basic types of antenna, one is the receiving antenna, which receives RF energy and delivers AC to electronic equipment, and other one is the transmitting antenna, which receives AC from electronic equipment and generates an RF field.[1]
In all wireless communication systems an antenna plays essential role of the equipments that uses radio system. It is employed in systems such as broadcasting, broadcast, two-way radio, communications receivers, cell phones, radar and satellite communications, as well as other devices such as Bluetooth-based devices, garage door openers, wireless microphones, wireless computer networks and baby monitors.[2 ], [5].
Usually an antenna consists of an array of metallic conductors or other elements, electrically connected (often through transmission) to the receiver or transmitter. A sinusoidal current of electrons made to force an antenna through a transmitter and creates an oscillating magnetic field around the antenna elements, while the electrons also create an oscillating electric field around the antenna elements. The antenna radiates these time-
varying fields into space as a moving transverse electromagnetic field wave. on the contrary, during receiving of an oscillating electric and magnetic fields of an incoming radio wave exert force on all the electrons in the antenna elements, causing them to move back and forth, creating oscillating currents in the antenna.
2 MICROSTRIP PATCH ANTENNA
The study of microstrip patch antennas has made great progress in recent years.
Compared with conventional antennas, microstrip patch antennas have more advantages and better prospects. They are lighter in weight, low volume, low cost, low profile, smaller in dimension and ease of fabrication and conformity. Moreover, the microstrip patch antennas can provide dual and circular polarizations, dual-frequency operation, frequency agility, broad band- width, feed line flexibility, beam scanning Omni directional patterning. In this paper we discuss the microstrip antenna, types of microstrip antenna, feeding techniques and application of microstrip patch antenna with their advantage and disadvantages over conventional microwave antennas. In high-performance aircraft, spacecraft, satellite, and missile applications, where size, weight, cost, performance, ease of installation, and aerodynamic profile are
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constraints, low-profile antennas may berequired. Presently there are many other government and commercial applications, such as mobile radio and wireless communications that have similar specifications. To meet these requirements, microstrip antennas can be used. These antennas are low profile, conformable to planar and non planar surfaces, simple and inexpensive to manufacture using modern printed-circuit technology, mechanically robust when mounted on rigid surfaces, compatible with MMIC designs, and when the particular patch shape and mode are selected, they are very versatile in terms of resonant frequency, polarization, pattern, and impedance. In addition, by adding loads between the patch and the ground plane, such as pins and varactor diodes, adaptive elements with variable resonant frequency, impedance, polarization, and pattern can be designed.
Microstrip Antennas Microstrip patch antennas Microstrip dipoles Printed slot antennas Microstrip Travelling wave antennas.[36], [38]
2.1 Basic Characteristics
Microstrip antennas received considerable attention starting in the 1970s, although the idea of a microstrip antenna can be traced to 1953 and a patent in 1955.
Microstrip antennas, consist of a very thin ( t<<λ0, where λ0 is the free-space wavelength) metallic strip (patch) placed a small fraction of a wavelength ( h << λ0, usually 0.003λ0 ≤ h ≤ 0.05λ0) above a ground plane. The microstrip patch is designed so its pattern maximum is normal to the patch (broadside radiator). This is accomplished by properly choosing the mode (field configuration) of excitation beneath the patch. End-fire radiation can also be accomplished by judicious mode selection. For a rectangular patch, the length L of the element is usually λ0/3 < L
< λ0/2. The strip (patch) and the ground plane are separated by a dielectric sheet (referred to as the substrate). There are numerous substrates that can be used for the design of microstrip antennas, and their dielectric constants are usually in the range of 2.2 ≤ εr≤ 12. The ones that are most desirable for good antenna performance are thick substrates whose dielectric constant is in the lower end of the range because they provide better efficiency, larger
bandwidth, loosely bound fields for radiation into space, but at the expense of larger element size.
Figure 1 Micro strip antenna and coordinate system.
Thin substrates with higher dielectric constants are desirable for microwave circuitry because they require tightly bound fields to minimize undesired radiation and coupling, and lead to smaller element sizes;
however, because of their greater losses, they are less efficient and have relatively smaller bandwidths. Since microstrip antennas are often integrated with other microwave circuitry, a compromise has to be reached between good antenna performance and circuit design. Often microstrip antennas are also referred to as patchantennas. The radiating elements and the feed lines are usually photo etched on the dielectric substrate. The radiating patch may be square, rectangular, thin strip (dipole), circular, elliptical, triangular, or any other configuration. Square, rectangular, dipole (strip), and circular are the most common because of ease of analysis and fabrication, and their attractive radiation characteristics, especially low cross-polarization radiation.
Microstrip dipoles are attractive because they inherently possess a large bandwidth and occupy less space, which makes them attractive for arrays. Linear and circular polarizations can be achieved with either single elements or arrays of microstrip antennas. Arrays of microstrip elements, with single or multiple feeds, may also be used to introduce scanning capabilities and achieve greater directivities. [39], [41]
2.2 Feeding Methods
A feed line is used to excite to radiate by direct or indirect contact. There are many different techniques of feeding and four most popular techniques are coaxial probe
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feed, micro strip line, aperture coupling andproximity coupling. There are many configurations that can be used to feed micro strip antennas. The four most popular feeds are the micro strip line, coaxial probe, aperture coupling, and proximity coupling. Coaxial probe feeding is feeding method in which that the inner conductor of the coaxial is attached to the radiation patch of the antenna while the outer conductor is connected to the ground plane. Advantages of coaxial feeding is easy of fabrication, easy to match, low spurious radiation and its disadvantages is narrow bandwidth, Difficult to model specially for thick substrate.
Micro strip line feed is one of the easier methods to fabricate as it is a just conducting strip connecting to the patch and therefore can be consider as extension of patch. It is simple to model and easy to match by controlling the inset position.
However the disadvantage of this method is that as substrate thickness increases, surface wave and spurious feed radiation increases which limit the bandwidth.
Aperture coupled feed consist of two different substrate separated by a ground plane. . On the bottom side of lower substrate there is a micro strip feed line whose energy is coupled to the patch through a slot on the ground plane separating two substrates. Proximity coupling has the largest bandwidth, has low spurious radiation. However fabrication is difficult. Length of feeding stub and width-to-length ratio of patch is used to control the match. Its coupling mechanism is capacitive in nature.
Figure 2 Typical feeds for microstrip antennas
3 FRINGING EFFECTS
Because the dimensions of the patch are finite along the length and width, the fields at the edges of the patch undergo fringing.
This is illustrated along the length in Figures for the two radiating slots of the microstrip antenna. The same applies along the width. The amount of fringing is a function of the dimensions of the patch and the height of the substrate. For the principal E-plane (xy-plane) fringing is a function of the ratio of the length of the patch L to the height h of the substrate (L/h) and the dielectric constant εr of the substrate. Since for microstrip antennas L/h >>1, fringing is reduced; however, it must be taken into account because it influences the resonant frequency of the antenna.
The same applies for the width. This is a non-homogeneous line of two dielectrics; typically the substrate and air.
As can be seen, most of the electric field lines reside in the substrate and parts of some lines exist in air. As W/h >>1 and εr>>1, the electric field lines concentrate mostly in the substrate. Fringing in this case makes the microstrip line look wider electrically compared to its physical dimensions. Since some of the waves travel in the substrate and some in air, an effective dielectric constant εreff is introduced to account for fringing and the wave propagation in the line. To introduce the effective dielectric constant, let us assume that the center conductor of the microstrip line with its original dimensions and height above the ground plane is embedded into one dielectric.
The effective dielectric constant is defined as the dielectric constant of the uniform dielectric material so that the line has identical electrical characteristics, particularly propagation constant, as the actual line. For a line with air above the substrate, the effective dielectric constant has values in the range of 1 <εreff<εr. For most applications where the dielectric constant of the substrate is much greater than unity (εr<<1), the value of εreff will be closer to the value of the actual dielectric constant εrof the substrate. The effective dielectric constant is also a function of frequency. As the frequency of operation increases, most of the electric field lines concentrate in the substrate. Therefore the microstrip line behaves more like a
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homogeneous line of one dielectric (only thesubstrate), and the effective dielectric constant approaches the value of the dielectric constant of the substrate. Typical variations, as a function of frequency, of the effective dielectric constant for a microstrip line with three different for low frequencies the effective dielectric constant is essentially constant. At intermediate frequencies its values begin to monotonically increase and eventually approach the values of the dielectric constant of the substrate.
4 TYPES OF ANTENNA
Antenna can be divided into following categories:
4.1 Wire Antenna
Awireless antenna is a normally radio antenna which consists of a long wire hanging above the ground. Length of wire does not tolerate a relation to the wavelength of the radio waves used, but is usually chosen more for convenience. The wire may be long straight or it may be tied back and forth between trees or walls just to get enough wire into the air; this type of antenna sometimes is called a zigzag antenna. Such antennas are usually not as effective as antennas whose length is shifted to resonance at the wavelength to be used. Random wire antennas are a type of monopole antenna and the second side of the dedicated transmitter or receiver antenna terminal must be connected to an earth ground.
They are widely used as receiving antennas on the short wave, medium wave, and long wave bands, as well as transmitting antennas on these bands for small outdoor, temporary or emergency transmitting stations, as well as in situations where more permanent antennas cannot be installed.[6], [8]
Figure 3 Wire antenna
4.2 Aperture Antenna
Antenna aperture or effective area is a measure of how effective an antenna is at receiving the radio waves power. The aperture is defined as the area oriented perpendicular to the direction of incoming radio waves, which intercepts the identical amount of power from the wave that is produced by the receiving antenna. At present Aperture antennas are more familiar to the layman than in the past because of the increasing demand for more smart forms of antennas and the use of more higher frequency signals. Antennas of this type are very useful for aircraft and spacecraft applications, because it may be more conveniently flush-mounted on the outer surface of the aircraft or spacecraft.
They can also be enclosed with a dielectric material to guard them from dangerous conditions of the surroundings.[9]
4.3 Microstrip Antenna
The basic structure of a Microstrip Antenna consists of a thin sheet of low-loss dielectric substrate, which is placed between two metal sides. One side which is completely covered is called the ground plane and the other side of partially metalized also known as the patch and derives the name of the antenna. The common structures of a patch antenna may be circular, rectangular or triangular. The major advantage of MSA are listed as follows:[10], [17]
(i) Small size and low weight (ii) Easy to handle
(iii) Large scale fabrication is possible (iv) Inexpensive
It also suffers from some draw backs like narrow bandwidth, low gain, large ohm loss, excitation of surface waves, radiation from the feed, low polarization purity, low power handling capacity.
Some of the lacunas of MSA can be overcome by employing the concept of array. When the discrete radiators are joined to form a single array, it directs to enhance the individuality like power handling capacity, beam scanning and also the gain. The elements of any array can be dispersed to form linear array, planner array or volume array. There are various ways of feeding that can be used to obtain definite characteristics. Single Input Single Output (SISO), Multi Input Multi Output (MIMO) are some common concepts. The need of present day communication
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requires a broadband, miniature antenna.The engineering approach to meet the requirements in case of MSA related to its polarization, widening the bandwidth and reducing the size of the antenna is addressed in the subsequent sections.
5 CONCLUSION
This paper shows the review and survey of techniques and design for the designing of efficient microstrip patch antenna. By using one of any above mentioned technique some of the limitations of conventional microstrip characteristics is improved. This review work is done on some characteristics implemented through different techniques.
Nevertheless, useful solution are still less and suffer from different problems like complexity of structure, reduced band width, reduction of gain etc. Hence, the author feels that further research and more work is needed in these areas. After searched the gap of research paper, reached at the point where is the a design has been discussed in this paper based on High Frequency Structure Simulator. In this design all the techniques will be used for analysis the parameters OF ANTENNA.
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